The present invention relates to solder reflowing methods and machines, and in particular to methods and machines for removing very small electronic components which have a very high pin density from a printed circuit board which has a large number of such component types in close proximity.
Various types of heat transfer fluids have been utilized to reflow solder so as to allow the removal of components from printed circuit boards. These include super-heated air, or nitrogen or other gas, liquid solder, direct mechanical contact with a heated object, such as a soldering iron or a hot plate. These methods are generally disadvantageous because they have a low efficiency of heat-transfer and their usage often results in excessively long heating times for the components and the boards, which causes thermal stresses in both the boards and the components, which may result in damage or failure of either, or both. In addition, the time for achieving removal is longer than optimum.
The combination of the use of a hot gas to reflow the solder for a multi pin component in a vacuum to control the placement or removal of a multi pin component is shown in two IBM Technical Disclosure Bulletins. The first is "Chip Removal by Hot Gas" by C. R. Tickner, Vol. 11 No. 7, December 1968, p. 875, and "Solder Reflow Tool" by C. Trollman, Vol. 11 No. 10, March 1969, p. 1298.
Another IBM Technical Disclosure Bulletin "Solvent Vapor Solder Reflow" by E. G. Dingman, Vol. 13 No. 3, August 1970, p. 639, indicates that a boiling solvent may be used to facilitate removal and resolder of electronic components. The present invention is able to utilize a liquid, or fluid, heat transfer material where the temperature of the fluid may be raised to a temperature sufficient to cause the solder to reflow, but the fluid does not have to be in a boiling state, although it could be if necessary.